(1) Field of the Invention
The present invention relates to a network looping detecting apparatus, and more particularly to a network looping detecting apparatus for detecting an instance of network looping.
(2) Description of the Related Art
One of IP network service interruptions is known as network looping which means a communication failure due to packets looping around between a plurality of network devices, e.g., routers, L3 switches, etc. Network looping is caused by faults such as wrong settings in network devices, e.g., Default Route setting mistakes, or hardware failures.
It may be possible to prevent network looping by confirming settings in all network devices of a network that needs to be checked for network looping. However, since uncontrollable settings according to routing protocols including BGP (Border Gateway Protocol), OSPF (Open Shortest Path First), and RIP (Routing Information Protocol) are widely used to cause network looping, it is difficult to prevent network looping simply by confirming network device settings. It has also been desired in the art to detect and eliminate network looping quickly when it occurs, as well as to prevent network looping in advance.
There have been available four methods, to be described below, for detecting network looping. According to the first method, the routing tables of network devices that are involved are checked to detect whether they will cause network looping. According to the second method, a measuring packet is sent to the network to be monitored to estimate whether network looping is occurring. For details, see, for example, “Detection and Analysis of Routing Loops in Packet Traces,” IMW (Internet Measurement Workshop) 2002, (Marseille), Nov. 6, 2002. The third method employs a packet capturing device to determine whether a packet is a looping packet or not for detecting network looping. For details, see, for example, “Delayed Internet routing convergence,” ACM SIGCOMM 2000, (Stockholm), Aug. 31, 2000. According to the third method, the packet capturing device is used to capture packets at all times and identify, as looping packets, those packets whose invariable parts such as a destination IP address and a source IP address remain unchanged and whose variable parts such as a TTL field and a checksum field according to IPv4 and a HopLimit field according to IPv6 are changed. The third method is based on the fact that the invariable parts of a looping packet are not changed and the variable parts thereof are changed by a recalculation each time the packet passes through a network device.
The fourth method uses an ICMP (Internet Control Message Protocol) TimeExceeded packet as a measuring packet or a packet to be captured for reducing the amount of data to be calculated, thereby reliably detecting network looping. The fourth method is disclosed in Japanese patent application No. 2003-326173.
The first method is disadvantageous in that because it refers to the routing tables of network devices, it lacks scalability and real-time processing.
The second method is problematic in that since a measuring packet is sent to the network to be monitored and an instance of network looping is only estimated from an increased packet loss, a packet delay time, and a tracing route change, the method is not reliable enough.
The third method operates excellently in real-time for detecting network looping, but is not scalable as a packet capturing device needs to be installed in the network to be checked.
The fourth method also lacks scalability because a packet capturing device needs to be installed to capture packets though ICMP TimeExceeded packets are employed.